- The collagen content and composition of collagens in
different age classes of shrimp were determined. Their
physical and chemical characteristics were investigated.
The interrelationship of shrimp size and muscle collagen
content to raw and cooked meat yield was established.
Total collagen content for three lots of round shrimp
with weights averaging 2.58±.39, 5.27±.55 and 7.72±.96 g was
determined to be 2.36, 3.35 and 3.47 mg collagen/g total
musculature N, respectively. Unformed collagen comprised
53.85, 35.52 and 0.86% of the total collagen content, respectively.
Maturation, as reflected by shrimp size, was
accompanied by a near linear increase in formed collagen.
A molecular weight of 310,000 for shrimp collagen was
determined using SDS gel electrophoresis. The accuracy of
this determination was compromised by limited mobility and
lack of standard reference proteins of appropriate molecular
weight, but did establish a molecular weight in a range
common to other collagens.
Variations in the amino acid composition of formed and
unformed collagen reflected the function of the tissues in
the musculature from which they were derived. Formed
collagen contained higher amounts of glycine, proline and
hydroxylysine than unformed collagen, providing a chemical
basis for its structural function in formed connective tissues.
Remaining amino acids, except histidine, glutamate
and arginine were contained in higher amounts in unformed
collagen. Unformed collagen also contained a substantial
amount of unidentified components which were suspected to
be amino sugar derivatives. Only trace amounts of these
components were found in formed collagen.
Shrimp collagen contained unusually low levels of glycine,
only trace amounts of hydroxyproline and substantial
quantities of tryptophan. Glycine and hydroxyproline are
important amino acids in mammalian collagens, but tryptophan
is usually not present. Shrimp collagen also contained
higher levels of threonine, tyrosine, hydroxylysine, valine,
methionine, leucine, isoleucine and phenylalanine than most
other reported collagens. These variations in amino acid
composition seem to reflect a requirement for a structural
protein possessing unique characteristics commensurate with
the anatomical structure of the species.
The yield (% dry wt.) of raw and cooked (100 sec;
101°C in steam) derived through hand peeling round shrimp,
was correlated (P>.001) in a positive manner by well defined
power functions. Raw meat yield (% dry wt.) declined during
ice storage in a linear (P>.001) manner at a rate dependent
upon shrimp size. The more rapid loss of solids from large
shrimp reduced yield differences as storage was extended.
Raw meat losses during ice storage ranged from 0.298 to
0.318 g raw meat dry matter/100 g round shrimp/day for 2.5
and 7.5 g shrimp respectively. Dry matter weight loss from
raw meat through the washing action of melting ice, was replaced
in a linear (P>.05-P>.005) manner with water to maintain
yield (% wet wt.) during storage. Ice storage expanded
cooked yield (% dry wt.) differences between shrimp sizes.
Meat losses through cooking mediated by ice storage, ranged
from 0.421 to 0.303 g cooked meat dry matter/100 g round
shrimp/day for 2.5 and 7.5 g shrimp, respectively.
The age class dependent content and composition of
collagens in the musculature of shrimp was reflected in the
recovery of raw and cooked meat. Meat from small shrimp
contained higher levels of unformed collagen which possessed
less dry matter and degraded more rapidly in ice storage.
Proteolytic action on elevated levels of unformed collagen
was not reflected in the rate of ice storage losses. But,
it markedly increased heat induced solubilization of solids
and enhanced moisture retention through steam precooking
over larger shrimp. Maturation of shrimp associated with
more formed and less unformed collagen reduced solids solubilization
and moisture retention through steam precooking.